1. Field of the Invention
The present invention relates to an abnormality monitoring device for a vehicle control system formed by interconnecting a plurality of control units of which objects to be controlled are different from one another by multiplex communication lines.
2. Description of the Related Art
In a vehicle control system employed in various vehicles, including motor vehicles, various controls of an engine, a transmission, suspensions, an air conditioner and the like are respectively assigned to a plurality of electronic control units (ECUs) including microcomputers and others, which are mounted on the vehicle. The ECUs are interconnected by communication lines, and control data transmission is performed among the ECUs, to thereby improve its total control performance.
In such a vehicle control system, it is important that each ECU carries out a self-diagnosis for its peripheral system, and additionally that the vehicle control system performs the monitoring operation to detect an abnormality in the overall control system. Conventionally, each of those ECUs mutually monitors an abnormality or abnormalities of the remaining ECUs by use of watchdog timers or by echo backing communication data.
Recently, in the vehicle, the amount of data transmitted between those ECUs increases. The data amount increase creates many problems, such as wire harness increase in size, wire layout restriction, and vehicle weight increase. To cope with those problems, there is a trend of adopting the multiplex communication technique for the communications among the ECUs. However, addition of the hardware for monitoring the abnormality, such as watchdog timer wires goes against the trend, and further increases the system cost.
The abnormality monitoring by the data echo-backing has also problems. It takes a long processing time. A traffic of the transmission path increases. As a result, the throughput of the overall system reduces.